1. Field of the Invention
The invention relates to a method of forming a saddle coil for a deflection coil assembly which in use deflects the electron beam or beams of a cathode ray display tube in one of two orthogonal directions, in which a saddle coil is formed by a conductive pattern on assembled insulating film parts. The invention also relates to a method of forming deflection coil assemblies and electromagnetic deflection units, and also to saddle coils, deflection coils assemblies and deflection units per se.
2. Description of the Related Art
A number of proposals have been made in the past to replace the conventional wire wound saddle coils used for electromagnetic deflection with cathode ray tubes by coils manufactured by the so-called printed circuit or printed wiring techniques. Some of these proposals have related to such coils for use with television pick-up tubes where the coil shape is relatively simple and does not require the particular shaping problems encountered with the neck-cone shaping of television display tubes. UK Patent Specification No. 1,398,388 attempts to overcome this problem by producing two saddle coils on an assembly of two parts comprising a cylindrical part and an annular part both parts carrying conductors with the conductors on the annular part interconnecting the conductors on the cylindrical part. A saddle coil produced in this way does not readily lend itself to multiple layer construction due to difficulties in providing the required connections between the cylindrical and annular parts and where the above specification refers to more than one layer this in fact relates to two layers each of which carries the deflection coil for a different deflection direction. The limitation placed by the shaping of the parts and hence on the saddle coils so produced makes it only suitable for use as deflection coils for monochrome cathode ray display tubes of limited deflection angle. Thus such saddle coils are not suited to wide angle monochrome display tubes nor to colour display tubes where the required deflection field places particular constraints on the shaping and construction of the saddle coils.